One of the former "Cavaliers miniers" (the name given to ancient railroad private coal mine in northern France). Some of these structures have now a true value of "biological corridor" and are classed as a part of the "ecological network of the "bassin miner". (By Lamiot (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons)

Biological corridor is the designation for a continuous geographic extent of habitat linking ecosystems, either spatially or functionally; such a link restores or conserves the connection between habitats that are fragmented by natural causes or human development. Such corridors are an important aspect in the preservation of species richness and biodiversity. There are different scales of biological corridors, but all share the same purpose of providing connections for species through fragmented landscapes. A biological corridor, alternatively termed habitat corridor, is used for the transportation functions of fauna and seed dispersal/propagation routes for flora and lower life forms. Specific elements of this transport for fauna include seasonal or migration movement, life cycle links, species dispersal, re-colonization of an area and movement in response to external pressures. These corridors are not always literally continuous, some acting as stepping stones that provide resting and feeding stops along migratory routes that may contain inhospitable territory. Managed areas adjacent to these corridors are called buffer zones. These zones extend the areas within which faunal species can travel or flora species can propagate.

Local riparian biological corridor likely created originally by prehistoric Alby Peoples wishing to enhance food production and ecosystem services in eastern coastal Oland, Sweden. Source: C. Michael Hogan
There are many different types of habitat that are suitable for these pathways; natural habitats including forests, grasslands, wetlands, coral reefs, and salt marshes; semi-natural habitats such as managed forests, small scale farms, reservoirs, tree plantations, and pasture land; habitat fragments such as perch trees and garden ponds; riparian zones, streams, lake shores, and coastline; and even artificial corridors, perches, or nest sites used to increase dispersal and maintain natural processes.

Hierarchy of Biological Corridors

Regional: These are primary pathways between large important areas of habitat. Ecological principles state that a corridor should be twice the width of the average home range of the species thought to be potential users of the corridor. Typically, regional corridors connect very large, intact areas, and are focused on connecting habitats for very large-scale species. They can be national and even continental in scale. Examples of regional biological corridors include the Mesoamerican Biological Corridor of Central America, the Yellowstone to Yukon Corridor of North America, and the Atherton Corridor of Australia.

Sub-regional: These are smaller connections, typically between large vegetated landscape features such as ridgelines and valley floors. Typically a sub-regional corridor links several protected areas into a cohesive network, and may cross one or more national boundaries. An example of a sub-regional biological corridor is the Vilcabamba Amboro Conservation Corridor in South America, linking the protected areas of Peru and Bolivia into a cohesive network.

Local: These corridors are less defined than large-scale corridors. Local corridors can be creek lines, gullies, wetlands, ridgelines and other features that connect one core area to another. These local corridors may be narrow, less than 50 meters wide, making them susceptible to edge effects, such as encroachment of edge species, invasive species, disease and habitat fragmentation.

Theory of Island Biogeography

The need for biological corridors is based on the theory of island biogeography. The theory states that species richness is directly related to an island’s size and it’s level of isolation from other landforms. Often, protected areas are “islands” of remnant natural vegetation surrounded by large expanses influenced by human activity. As corridors connect these fragmented “islands” of vegetation, species richness can increase with the size of the usable habitat. Theoretical treatments have been developed to quanify the connectivity of fragmented habitats. (Chetkiewicz et al. 2006)

The theory of habitat connectivity indicates that species with greater degrees of habitat or corridor specialization will have greater response to habitat corridors than non-specialists; additionally smaller rather than larger animals are likely to respond to habitat connectivity due to the ability to match organism requirements to landscape scale. While experimental data are insufficient to validate all theoretical arguments, the limited data supports these notions of differential organism response. (Crooks and Sanjayan. 2006)

Corridor parameters

Not any piece of real estate will provide an effective biological corridor. Key factors that must be considered in producing a robust corridor include: (a) appropriate geometry of the corridor; (b) suitability of the plant association within the corridor to support the floral and faunal uses (Hilty et al. 2006) of the corridor; (c) suitability of abiotic factors within the corridor; and (d) absence of any alien species that could disrupt the metabolisms or functions of native species intended to use the corridor.

Chief geometric needs stem from migration and dispersal to be conducted in a time scale appropriate to the needs of the species supported, without undue exposure to alien species or edge effects inherent in the corridor. For example, in the case of seasonal land migration of certain salamanders, if the length of the corridor is greater than the characteristic travel capability of the salamander, then the corridor is ineffective in providing additional aestivation opportunities. (Hogan et al. 1974) Furthermore, careful attention must be placed on edge effects, where habitat value may be altered due to seed desiccation, windthrow or exposure to predators lurking at the habitat edge.

Presence of compatible plant associations within the corridor may be vital, since matching the flora types with cover and food requirements may be requisite for the survival of the intended beneficiary species. In the case of faunal movement, even the traction and runway characteristics of the micro-habitat may be key to transportation, especially for smaller fauna. Appropriateness of the plant association influences the outcome micrometerology of the corridor, which factors affect metabolic and survival needs of species that may use the corridor. Specific plants must be present to support the dietary needs of herbivores that will use the corridor, and plant densities and canopy structure must match the disparate needs of varied faunal requirements for such activities as perching, resting, hiding, burrowing and preying. .

Abiotic factors are also important to match beneficiary species habitat requirements. Besides microclimate needs alluded to above, the availability of water, the soil and water pH, soil texture and compaction, soil nutrients and the absence of harmful chemicals such as pesticide residues are important elements of corridor success. These factors become particularly important for flora gene pool flow, since plants typically must take root and survive for many generations in order to connect or rescue the linked habitat. The match of plant species can be vital to support herbivores that consume significant amounts of nutrition in their passage through the corridor; this match is particularly critical for butterflies and other arthropods that use plants as host specie in a life cycle role. Interference with migration from alien species is self evident in cases where the aliens produce excessive predation or competition with the intended beneficiary species of the corridor.

Example Large Scale Corridors

Yukon Territory, Canada (Wikimedia Commons)

Yellowstone to Yukon

Yellowstone to Yukon (Y2Y) is a conservation initiative dedicated to encouraging and facilitating collaboration between groups working on conservation efforts throughout the Y2Y region. The Y2Y initiative works on connecting fragmented land from the Yukon Territory in Canada to Yellowstone National Park in Wyoming in the United States.

This region spans 1.3 million square kilometers (502,000 miles), is 3,200 kilometers (1,988 miles) long, 500-800 kilometers (300-500 miles) wide, and covers area in Washington, Oregon, Idaho, Montana, and Wyoming in the United Sates; and British Columbia, Alberta, and the Yukon and Northwest Territory in Canada.

The objectives of the Y2Y initiative are to identify Priority Areas for conservation efforts based on current scientific research and identify threats to conservation. They also seek to promote education and awareness among inhabitants of this area of peaceful ways to coexist with wildlife found in the region. This area was chosen because it represents the largest remaining intact mountain ecosystem. The area from Yellowstone to Yukon also contains much of the best remaining habitat for some of North America’s threatened species including grizzly bears, wolves, wolverines, lynx, and some native fish. It is a unique area that is large enough to encompass an environment in which climate change adaptations can be made as time goes on. The geographic variety and biodiversity of the region allows for these adaptations.

The Y2Y founders and scientists have determined that the most effective conservation strategy should cover areas of land, sea, and sky. Their efforts are therefore concentrated on grizzly bear, avian, and aquatic conservation. The grizzly bear is thought to be a key species in this area, therefore these conservation strategies can be a model for future efforts for other species.

Threats to connectivity exist in this region. Resource extraction is facilitated by the cutting of roads through these important areas and causes further fragmentation. This includes projects involving mining, logging, oil, and gas extraction. Construction of paved roads and railroads also causes fragmentation. Other threats include improper disposal and management of human garbage and climate change. As climate change shifts the home ranges of certain species, efforts will need to be made to ensure that pathways to and from this new habitat remain available.

Algonquin to Adirondack

The Algonquin to Adirondack (A2A) Conservation Association is a group dedicated to connecting a fragmented area of habitat from Ontario, Canada to the Adirondacks in New York. They have numerous ongoing projects aimed at learning more about the area and identifying Priority Areas. The Gananoque River Watershed Project in Ontario is an inventory of the species found in an around the Gananoque River. Through this research, the A2A hopes to find if sensitive species exist in the area and the best way to manage corridors through this area. Another project under the Gananoque River Watershed Project is research on Lower Beverly Lake. This project is ensuring that the shorelines in this area are healthy, which will contribute to the habitat of any sensitive species in and around the lake. The A2A also have outreach programs for the public encouraging them to make their land “wildlife friendly” and advocating peaceful human-wildlife interactions. The objectives of this organization are similar to the Y2Y initiative. This area is the most important area for biodiversity east of the Rocky Mountains.

Conclusion

Creating and maintaining biological corridors are important steps towards restoring natural habitats that have been fragmented by natural and human induced processes. By re-establishing and supporting biodiversity, many species are given an opportunity to continue existence in the wild. Conservation organizations continue to research and identify areas that are suitable for these connections, and educate the public about methods of creating habitat corridors.